A swamp always has a coastline.

I don't ever recall ever having a totally landlocked swamp. Don't think it happens honestly.

My current game I have found a lot of swamps but they are all tiny. Strips of swamp with nothing much in them, Not bad for harvesting resources but its been a killer for iron.

Out of the five-four crypts I have found they each were in their own smallish swamp area. All over the map in tiny spots.

Even found two bonemass altars in tiny swamps with no crypts ha ha.

Kind of crazy honestly.. at some point I am expecting to stumble upon a giant swamp with hundreds of crypts in it.